Canine DUXC isoforms and functional similarity to human DUX4 [RNA-seq]

Human DUX4 and mouse Dux transcription factors are normally expressed in the germ line and early embryonic cells where they activate the cleavage stage genes. The misexpression of DUX4 in skeletal muscles causes Facioscapulohumeral dystrophy (FSHD). In primates and rodents, DUX4 and Dux arose from retrotransposition of the mRNA from the ancestral intron-containing DUXC, which is not found in these species, and whether it has similar roles in the cleavage stage and FSHD as DUX4 and Dux are unknown. Here, we identified two isoforms of DUXC in canine testis tissues: One encodes the canonical double homeodomain (DUXC) similar to DUX4/Dux, and one contains an extra exon that disrupts the conserved amino-acid sequence of the first homeodomain (DUXC-ALT). We expressed DUXC and DUXC-ALT in canine skeletal muscle and found that the expression of DUXC induced retrotransposons and pluripotent programs similar to DUX4 and Dux, whereas DUXC-ALT did not robustly activate genes in these assays. Overall design: Determined the transcriptome of DUXC and DUXC-ALT by using a system that parallels tissue culture models of the human DUX4 transcriptome, forced expression of DUX4, DUXC, and DUXC-ALT transcription factors in cultrued canine skeletal muscle cells. We generate three doxycycline-inducible stable canine myoblast cell lines in which addition of doxycycline to the cell culture medium caused expression of three transcription factors and Luciferase (as a negative control).